In many oil fields, the oil bearing formation comprises an oil bearing zone, a gas cap zone, and/or an aqueous zone. Many of these fields produce a mixture of hydrocarbons (e.g., oil and gas) and water wherein the ratio of the hydrocarbons to water decreases as the field ages. This is a result of many factors well known to those skilled in the art.
The produced stream of hydrocarbons and water is typically separated into an oil portion, a gas portion, and a water portion at the surface. The water portion may be disposed of in any desirable manner; for example, it may be treated and put into a surface water reservoir such as a pond, injected into the formation, or the like. The gas portion may be marketed as a natural gas product, injected into the gas cap to maintain pressure therein, or the like.
Water and gas are typically separated from the oil at the surface. During production of the stream of hydrocarbons and water through the wellbore, the water portion contributes significantly to the weight of the column of fluids in the wellbore, thereby significantly increasing the formation pressure required to produce the fluids without pumping. For fluids to be produced upwardly through the wellbore, the formation pressure must exceed the hydrostatic fluid pressure. As the formation ages, the formation pressure decreases until it is insufficient to overcome the hydrostatic fluid pressure and produce fluids from the formation to the surface without pumping or the like.
It is thus desirable to reduce the weight, and the consequent hydrostatic pressure, of the column of fluids in the wellbore and, thereby, increase the productive life of the subterranean formation so that greater quantities of oil may be produced at lower costs from a formation. This has been achieved by positioning a downhole separator and an electrically powered pump downhole in a wellbore. The separator is configured to separate at least a major portion of the water from the hydrocarbons, and the electrically powered pump then injects the water downhole into the formation so that the water is not produced with the hydrocarbons. It is, however, very expensive to install an electrically powered pump and, furthermore, such an electrically powered pump requires significant maintenance and, consequently, production must be periodically discontinued to maintain or replace the motor, resulting in increased costs, production down time, and lost revenues.
Accordingly, a continuing search has been directed to the development of a system and method in which water can be reliably separated and injected into the formation more economically than is possible with an electrically powered pump.